This invention relates to an improved method for multi-stage washing surfaces of metallic products such as metal cans to remove a treating liquid from said surfaces.
When bodies of metal cans, for example, two-piece cans known as drawn and ironed cans (DI cans) are to be fabricated, a large amount of a cooling agent is applied over the inside and outside surfaces of side walls of the can in ironing the side walls, and thus it is necessary to remove the cooling agent attached to the surfaces of cans with bottoms after the shaping. Thus, a treating liquid is applied to the cans and successively the cans are washed off the treating liquid.
FIG. 1 shows a typical apparatus for washing off the treating liquid from the surfaces of such metallic products as described above, where an arrow mark Z shows the advancing direction of belt conveyor 5 and metal cans A placed on the belt. Belt 5 and metal cans A together will be hereinfter referred to as "material to be treated", because the treating liquid is applied to and retained on both said cans and said belt. In the advancing direction of the material to be treated there are treating tank 1 filled with treating liquid 11 and washing tanks 2, 3, and 4, each, filled with washing liquids 12, 13 and 14, which contain the treating liquid as a result of washing the resulting treated material, and provided in series in succession to treating tank 1, where tank 4 will be hereinafter referred to as furthermost washing tank in the advancing direction Z, and tank 2 adjacent to treating tank 1 as nearest washing tank.
Numerals 6, 7, 8, and 9 are pumps for pumping the liquids each filled in tanks 1, 2, 3 and 4, numerals 16, 16' 17, 17', 18, 18', 19 and 19' are nozzles for spraying the treating liquid and the washing liquid each pumped up by pumps 6, 7, 8 and 9 over the material to be treated or the treated material in the respective zones of the tanks, numerals 21, 22, 23 and 24 are conduits for passing the liquids by respective pumps 6, 7, 8 and 9 to nozzles 16, 16', 17, 17', 18, 18', 19 and 19', and numeral 20 is a pump for supplying a fresh washing liquid such as fresh water to tank 4 through conduit 25.
In the foregoing apparatus, metal cans A advance together with belt conveyor 5 in the arrow direction Z, and treating liquid 11 is applied over the material to be treated from nozzles 16 and 16' in the zone of tank 1, and the resulting treated material with the treating liquid, that is, cans A and belt 5, is washed with washing liquid 12 in tank 2 in the zone of said tank 2 through nozzles 17 and 17', and the treating liquid on the treated material is diluted. In the zone of tank 3, washing liquid 13 in said tank 3 is sprayed over the treated material through nozles 18 and 18', whereby the treating liquid on the treated material is further diluted. Also in the zone of tank 4, washing liquid 14 is sprayed over the treated material likewise through nozzles 19 and 19', and the treated material is sent to a successive step without any substantial treating liquid thereon.
As is obvious from the foregoing description, the treating liquid falls into washing tanks 2, 3 and 4 from the washed treated material, though the treating liquid is diluted, and the diluted treating liquid, though at a considerably lower concentration than that of the treating liquid 11 in treating tank 1, is entered and retained in the washing liquid in the respective washing tanks. The concentration of the treating liquid in the washing liquids in the respective washing tanks 2, 3 and 4 is highest in washing liquid 12, lower in washing liquid 13, and lowest in washing liquid 14. To prevent an increase in concentration of the treating liquid in the respective washing tanks, fresh liquid such as fresh water is supplied to furthermost tank 4, and washing liquid 14 is supplied in an amount equal to that of the supplied fresh liquid from tank 4 to adjacent tank 3 placed after tank 4 in the advancing direction Z. Furthermore, washing liquid 13 is supplied in an amount equal to that of the supplied fresh liquid from tank 3 to adjacent tank 2 placed after tank 3. Washing liquid 12 is discharged in an amount equal to that of the supplied fresh liquid through conduit 10 from nearest tank 2.
A means for supplying the washing liquid from the individual tanks to tanks placed after said individual tanks can be any appropriate one such as an overflow system, a pumping system, etc.
Volumes and concentrations of the washing liquid in washing tanks 2, 3 and 4 can be kept constant by supplying fresh liquid to the furthermost washing tank and discharging the washing liquid from the nearest tank, and a constant washing effect can be obtained thereby.
Advantages of said multi-stage washing system is to reduce the amount of supplied fresh liquid and attain an equal washing effect to that when the entire washing liquid is stored in a single washing tank and applied to washing, and also to facilitate waste liquid treatment, because only a small amount of washing liquid with a high concentration of the treating liquid, which is equal to the amount of the supplied fresh water is discharged from the system.